Self-spacing pleated filter insert

ABSTRACT

A replaceable, self-spacing, pleated, filter insert that can be easily installed in a reusable filter frame without the aid of a secondary spacing structure includes reversibly collapsible and expandable filter media including a plurality of pleats that expand uniformly when the filter is expanded. When the filter is expanded to the length of the filter frame, the filter is under tension and behaves like a spring, thereby allowing the length of the filter to be readily adjusted to match the length of the frame and allowing the pleats to be aligned with corresponding ribs provided in the frame.

FIELD

The present invention relates generally to filters and, moreparticularly, to a removable filter insert that is inserted into areusable frame.

BACKGROUND

Many conventional residential heating and cooling systems include adisposable filter. These filters include a frame, a fibrous filtermaterial, and a mesh screen or the like that supports the filtermaterial. After a period of use, these filters become dirty or cloggedand must be replaced. This is accomplished by replacing the entirefilter assembly with a new filter and discarding the old one. Dependingon the use of the filter, replacement may be required several times ayear. Because the frame and screen are discarded with the assembly eventhough it is only the filter material that is no longer functional,there is unnecessary waste and cost associated with such filters. Inaddition, because these filters are rather bulky, they are oftenpurchased as they are needed rather than keeping a large supply on hand.Because purchasing a new filter is not always convenient, replacementcan be delayed resulting in reduced system performance.

Conventional filters are typically formed from a soft, limp, flexiblematerial that lacks sufficient structural integrity to counteract anapplied force. As a result, such filters, when pleated, do notsignificantly recover after being expanded and do not significantlyexpand after being collapsed. In addition, such filters do not expandwith uniform pleat spacing. Consequently, if one attempts to installsuch a pleated filter in a frame having ribs designed to nestle betweenthe pleats and thereby maintain equal spacing and provide additionalsupport for the filter, it is difficult to match the pleats of thefilter with the ribs. Such filters must therefore include a secondarysupport structure to ensure uniform spacing of the pleats during theinstallation process. Such support structures, however, add to thematerial and manufacturing cost of such filters.

Filter assemblies with frames and removable filter elements are known inthe prior art. U.S. Pat. No. 6,033,453 (Weddell, III), for example,discloses a reusable frame support rack for supporting and retaining anoutstretched, replaceable pleated media filter core. The frame includesa pair of longitudinal angles extending between a pair of transverseangles which carry a flat expanded metal support or reinforcementsystem.

SUMMARY

Previous filters, however, suffer from certain limitations anddrawbacks. There exists a need, therefore, for a self-spacing pleatedair filter without a secondary support structure that can be readilyexpanded to fit in a reusable filter frame, whereby the filter, whenexpanded, has uniform spacing and desirable cross-web stability.

It would therefore be desirable to provide a self-spacing, reversiblycollapsible and expandable, pleated air filter that does not include asecondary support structure, has uniform spacing and cross-web stabilitywhen expanded and inserted into a reusable filter frame, and can becollapsed for compact shipping, storage, and disposal.

The present invention provides a replaceable, self-spacing, pleated,filter insert that can be easily installed in a reusable filter framewithout the aid of a secondary spacing structure. The filter insertcomprises a reversibly collapsible and expandable filter media includinga plurality of pleats, each pleat being defined by a fold line thatdefines a pleat tip and a pair of adjacent panels. When the filter isexpanded to the length of the filter frame, the filter is under tension,and when the filter is expanded to a length greater than the length ofthe filter frame, the filter will behave like a spring and exhibit somedegree of elastic recovery.

In another aspect, the invention provides a replaceable, self-spacing,pleated filter insert comprising reversibly collapsible and expandablefilter media including a plurality of pleats, each pleat including afold line defining a pleat tip and a pair of adjacent panels, whereinthe filter has a fully expanded length, and wherein when the filterinsert is expanded to greater than 80% of the fully expanded length, thefilter insert will be under tension such that when the filter insert isreleased, the filter insert will return to a length that is less thanthe fully expanded length.

In another aspect, when the filter insert is arranged vertically andextended to its fully expanded length and released, the filter insertreturns to a length that is no greater than 80% of the fully expandedlength. In another aspect, when the filter insert is collapsed to itsfully collapsed length and thereafter allowed to expand freely, thefilter insert expands to a length 400% greater than its fully collapsedlength.

In a specific aspect, the filter is an air filter constructed from afibrous nonwoven media formed of a thermoplastic polymer such aspolypropylene. In another aspect, the filter pleats are formed by heatsetting. In other aspects, the filter media may have one or more of thefollowing characteristics: a basis weight of 50–80 grams per squaremeter (g/m²), a permeability of 690–1024 cubic feet per minute (cfm),and a thickness of 0.5 to 0.63 millimeters (mm). In yet another aspect,the filter may include attachment members along opposed first and secondends of the media to facilitate securing the filter to the frame.

Advantages of various aspects of the invention include elimination of asecondary spacing structure, thereby reducing material costs andsimplifying the manufacturing process, providing a filter that is undertension and behaves like a spring when expanded to the length of thefilter frame into which it is to be installed, thereby allowing thelength of the filter to be readily adjusted to match the length of theframe and allowing the pleats to be aligned with corresponding ribsprovided in the frame, and providing a pleated filter that expandsuniformly and evenly with sufficient cross-web stability to preventfolding or collapsing of the filter in the cross-web (i.e. transverse)direction during the installation process, thereby improving handlingand installation of the filter insert into a frame.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described with reference to theaccompanying drawings, in which:

FIG. 1 is a perspective view showing a reusable filter frame with areplaceable filter insert according to the invention;

FIG. 2 is a sectional view taken along line 2—2 of FIG. 1;

FIG. 3 is a sectional view taken along line 3—3 of FIG. 1;

FIG. 4 is a perspective view showing the filter installed in a closedfilter frame;

FIG. 5 is a sectional view taken along line 5—5 of FIG. 4;

FIG. 6 is a perspective view of the filter in its partially expandedcondition;

FIG. 7 is a sectional view taken along line 7—7 of FIG. 6;

FIG. 8 is a side sectional view of the filter in its fully expandedcondition; and

FIG. 9 is a side sectional view of the filter in its fully collapsedcondition.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numerals refer tolike or corresponding parts throughout the several views, FIGS. 1–5 showa reusable filter frame 2 including a base 4 and an optional cover 6 foruse with a removable, self-spacing, pleated filter 8 having anappropriate size and configuration to fit into the base 4.Alternatively, the function of the base 4 and cover 6 may be reversed sothat the filter 8 is arranged in the cover 6 and the base 4 is closedwith the cover 6. The filter frame 2 has a generally planar rectangularconfiguration and is particularly suited for use in an air duct orfurnace of a residential air handling system.

The filter 8 generally includes filter media 10 having a plurality ofpleats 12. The filter 8 is described more fully below with reference toFIGS. 6–9.

The base 4 and cover 6 include perimeter structures 4 a, 6 a,respectively, having corresponding first ends 16, 18 and second ends 20,22, respectively, and first sides 24, 26 and second sides 28, 30,respectively. A plurality of equally spaced transverse ribs 32 extendfrom the first side 24 of the base 4 to the second side 28 of the base 4and mesh with the expanded pleats 12 to provide additional support forthe filter media 10 and maintain uniform spacing of the pleats 12 afterinstallation and during use. To provide complete and uniform spacing ofeach pleat 12, it is desirable that the ribs 32 be continuous across theentire width of the base 4, other than discontinuities that may berequired as part of the molding process, and have a uniform height. Inaddition, the number of ribs 32 preferably corresponds to the number ofpleats 12 on the downstream side of the filter 8 so that one rib 32 isarranged in each downstream pleat opening. The ribs 32 may be moldedwith the perimeter structure 4 a of the base 4 or they may be providedas wires, dowels, or other members that are attached to the perimeterstructure 4 a of the base 4.

The base 4 also optionally includes a plurality of longitudinal rails 34extending from the first end 16 to the second end 20 that combine withthe transverse ribs 32 to form a grid structure. The ribs 32 and rails34 can be formed as separate structures or as a unitary structure. Therails 34 are shown with optional triangularly-shaped spacer portions 34a (FIG. 2) that generally follow the contour of the filter pleats 12,thereby maintaining the spaced structure of the pleats 12. Each spacerportion 34 a includes a base 36 along the rail 34 and an apex 37 (FIG.5) adjacent a corresponding rib 32. The ribs 32 and rails 34 arepreferably formed of a synthetic plastic material such as ABS(acrylonitrile butadiene styrene) or HIPS (high impact polystyrene) butmay also be formed of other conventional materials such as wire or flatmetal fins.

The cover 6 contains a central opening 38 that allows air to flowthrough the frame 2 to the filter 8 so that contaminants can be removedfrom the air stream. The cover 6 engages the periphery of the base 4 tosecurely retain the filter 8 in the frame 2 and to prevent air fromflowing around the filter 8. The base 4 and cover 6 are pivotallyconnected along their associated second sides 28, 30, respectively, viahinge members 40 (FIG. 4) in the form of flexible straps. In thismanner, the frame 2 is movable between an open condition (FIG. 1)wherein the base 4 and cover 6 first side edges 24, 26, respectively,are displaced to allow the filter 8 to be installed in or removed fromthe frame 2, and a closed condition (FIG. 4) wherein the base 4 andcover 6 first side edges 24, 26 respectively, are engaged to enclose thefilter 8 in the frame 2. It will be recognized that any conventionalhinge may be used to connect the base 4 with the cover 6. Alternatively,the frame 2 may have a single-piece unitary construction wherein thebase 4 and cover 6 are joined by a living hinge, formed, for example, byinjection molding. It will be recognized that the base 4 and cover 6 mayalso be formed as two separate pieces that snap together or otherwiseinterlock.

A pair of optional latches 42 (FIG. 4) each including a flexiblecantilevered bar member 44 (FIG. 1) that snap fits over an alignedprotrusion 46 (FIG. 1) are provided to maintain the frame 2 in itsclosed condition. Other conventional closures or mechanical fastenerssuch as hook and loop, elastic bands, locks, or the like may also beused.

The cover 6 may also optionally include transverse and/or longitudinalsupport bars (not shown) similar to those provided in the base 4 thatserve to further retain the filter media 10 in the frame. Such supportbars would prevent the filter media 10 from ballooning out of the framein case the frame is inadvertently inserted backward in an air duct.When inserted backward, the filter will not perform properly because thepleats are not supported by the ribs 32 and will therefore tend tocollapse in use, but the filter media will be retained in the frame 2 sothat any damage to the system is avoided.

To ensure that the frame 2 is installed correctly in the air duct withthe cover 6 upstream and the base 4 downstream so that air travelssuccessively through the cover 6, the filter 8, and the base 4, a visualindicator 47 is provided on the frame 2 showing the proper orientationof the frame relative to the direction of the air flow. Additionalinstructions may be provided to ensure the frame is properly oriented inthe air duct.

Protrusions 48 provided in the first 16 and second 20 ends of the base 4serve as securing mechanisms to attach the filter 8 to the base 4 whenthe filter 8 is installed in the frame 2. Each protrusion 48 engages analigned hole 50 contained in the first 18 and second 22 ends of thecover 6. Other suitable securing mechanisms include adhesive, hook andloop fasteners, clips, clamps, clasps, hooks, or the like.Alternatively, the filter 8 may be secured in the frame 2 by simplycapturing or pinching the ends of the filter between the base 4 and thecover 6.

The frame 2 is generally intended as a frame for a residential airfilter for use in, for example, a furnace, an air return duct, a windowair conditioning unit, or a kitchen range hood. Accordingly, the frame 2generally has a depth or thickness of ½ inch to 5 inches, preferablybetween ¾ inch to 1¼ inches, and more preferably approximately an inchthick. The height of the frame 2 is generally between 5 inches and 24inches, and preferably between 10 inches and 20 inches. The width of theframe is generally between 10 inches and 40 inches, and preferablybetween 20 inches and 30 inches.

To facilitate installation and removal of the frame 2 from an air duct,indentations 52 are provided in the ends 16, 20 of the base 4 and side26 of the cover 6. The indentations provide a narrow gripping regionalong the periphery of the frame that can be readily grasped by a userduring the installation and removal process.

Referring now to FIGS. 6–9, there is shown in greater detail thereplaceable, self-spacing, pleated filter insert 8 adapted for placementin the filter frame 2. “Self-spacing” refers generally to the ability ofthe filter insert 8 to be readily expanded and arranged in the frame 2having equally spaced transverse ribs 32 without the aid of a secondaryspacing structure. In certain aspects, it may also refer to the abilityof the filter to expand uniformly, or the tendency of the filter toexpand from its fully collapsed state. Uniform spacing of the pleatsrefers to the pleats expanding in a generally even fashion, whereby thedistance between adjacent pleat tips is generally equal and constantalong the entire length of the expanded filter. In another aspect of theinvention, “self-spacing” refers to a pleated filter that expands to atleast 500% of its fully collapsed length when permitted to expandfreely.

The filter 8 includes reversibly expandable and collapsible pleatedfilter media 10 having an inlet face 54 and an outlet face 56. Thefilter may be constructed from a self-supporting media, which wouldallow the filter to be used with a filter frame that does not includeribs 32. The reversibly expandable and collapsible construction allowsthe filter 8 to be collapsed to a compact form for shipping and storageand to later be expanded to an appropriate length for placement in andattachment to the frame 2. This construction also ensures reliableuniform down web spacing and cross-web stability, which aid handling andinstallation of the filter 8.

The media 10 includes a plurality of pleats 12 each including a foldline 60 defining a pleat tip 62 and a pair of adjacent panels 64. Thespacing distance 66 between successive pleat tips 62 depends of the sizeof the filter but generally ranges from about 2 millimeters to about 40millimeters. For most applications, however, the spacing distance 66between successive pleat tips 62 is preferably at least 5 millimetersand, more preferably, at least 8 millimeters. Pleat depth and thethickness of the filter 10 is typically about 1 centimeter to about 10centimeters (0.4 inches to 4 inches). For HVAC applications, the lengthand width of the filter 10 is typically 30.5 centimeters×30.5centimeters (12 inches×12 inches) to about 50.8 centimeters×76.2centimeters (20 inches×30 inches).

Optional elongate attachment members 70 are provided along opposite ends72, 74 of the filter 8 parallel to the fold lines 60. The attachmentmembers 70 preferably have a stiffness greater than the stiffness of thefilter media 10. The attachment members 70 provide the ends 72, 74 ofthe filter 8 with increased stiffness, thereby improving thehandlability of the filter 8 and allowing the filter 8 to be expandedmore easily and uniformly. In addition, the attachment members 70provide the ends 72, 74 with increased strength and rigidity so that thefilter 8 can be quickly and easily attached to the base 4 of the frame2.

Optional holes 76 that mate with protrusions 48 (FIG. 1) are provided inthe attachment members 70 and serve to attach the filter 8 to the base 4and maintain the filter 8 in its expanded condition when the filter 8 isplaced in the base 4. To ensure the filter 8 is properly oriented in theframe 2 during installation, the holes 76 and corresponding protrusions48 may be provided in an asymmetric pattern that allows the filter 8 tobe attached to the frame 2 in only one orientation. Other conventionalmeans for attaching the filter 8 to the frame 2 such as pinching theattachment members 70 between the base 4 and cover 6, hook and loopfasteners, adhesive, clips, clamps or the like may also be used. Theattachment members 70 may be formed of any suitable material includingmetal foils, paperboard, cardboard, chipboard, synthetic plasticmaterials including plastic film, or multiple layers of filter mediafolded over and laminated together.

The filter media 10 used to construct the filter insert 8 is relativelystiff and preferably self-supporting, and may also be electrostaticallycharged. By “self-supporting” it is meant that the media generallymaintains its shape when subjected to an air stream. Thus, whether themedia is self-supporting depends on the physical properties of the mediaitself, the geometry or construction of the media, and the conditions towhich the media is subjected in a particular end use application.

Generally, media having a Gurley stiffness of greater than 50 milligramsfor a sample size having a width of 2 inches and a length of 1.5 inchesand, more specifically, having a Gurley stiffness of greater than 100milligrams for such a sample size would be self-supporting for typicalresidential applications. For media having stiffness values less thanthis value, whether the media is self-supporting depends on theconstruction of the media and on the end use application. If the mediais self-supporting, the support ribs 32 (FIGS. 1 and 2) are not berequired because the media will maintain its shape when subjected to theair stream. Even if the filter media is self-supporting, however,support ribs 32 are preferably provided to improve the stability andoverall performance of the filter.

In accordance with a characterizing feature of the pleated filter insert8, when it is expanded to the length of the frame 2, the filter insert 8is under tension. That is, the pleated structure will tend to draw thepleats together, thereby causing the filter to return to a shorterlength. In accordance with another aspect of the invention, when thefilter insert 8 is expanded to a length that is greater thanapproximately 80% of its fully expanded length (as illustrated in FIG.8), the filter insert 8 will be under tension such that when the filterinsert is released and allowed to return to its equilibrium length, thefilter will return to a length that is less than its fully expandedlength, and preferably to a length that is less than the length of theframe 2.

As shown in FIG. 8, the filter insert's fully expanded length is thelength produced when the filter insert 8 is expanded such that thepleats are generally coplanar and the filter insert takes the form of agenerally flat sheet. Attempting to expand the filter insert 8 beyondits fully expanded length will place the filter media 10 itself undertension and will ultimately cause the media to tear or rupture.

Thus, when the filter insert 8 is expanded to a length that is greaterthan the length of the filter frame 2, the filter insert 8 will exhibitsome degree of elastic recovery and will tend to recoil to a length thatis less than the length of the filter frame 2. That is, the filterinsert 8 will behave like a weak spring. The construction of the filterinsert 8 also allows it to expand evenly and uniformly. In addition, thefilter insert 8 has sufficient cross-web stability to prevent the filterinsert 8 from folding or collapsing transversely. These characteristicsfacilitate installation of the filter insert 8 into the frame 2 byallowing a user to gently move the ends of the filter insert 8 apart ortogether to match the length of the frame 2, and by allowing the user tofeed the pleats into the spacing ribs 32 of the frame, if present.

In another aspect, when the filter insert 8 is arranged vertically andextended to its fully expanded length and released, the filter insert 8will return to a length that is no greater than 80% of the fullyexpanded length. And when the filter insert 8 is collapsed to its fullycollapsed length (as illustrated in FIG. 9) and then allowed to expandfreely, the filter insert 8 will expand to a length that is 400% greaterthan the fully collapsed length. In its fully collapsed condition,adjacent pleats of the filter insert 8 lie face to face in fullycontacting and overlapping relation.

The particular filter media selected for the filter insert 8 is notcritical to the invention hereof, so long as it can be used to produce afilter insert having the desired characteristics when pleated. Thefilter insert 8 may be constructed, for example, from nonwoven fibrousmedia formed of thermoplastics or thermosetting materials such aspolypropylene, linear polyethylene, and polyvinyl chloride. The filterinsert 8 generally has a basis weight of 50 to 80 g/m², a tensilestrength of 57 to 95 lbs (253 to 423N), a tensile elongation of greaterthan 60%, a thickness of 0.5 to 0.63 mm, a pore size of greater than 212microns. In addition, to produce a pleated filter having the desiredspringiness, the pleats may be formed by heat setting. Heat setting wasfound to increase the tension or tightness of the pleated structure ofthe filter insert 8, which may be desirable when using certain media.

A suitable filter insert 8 may be constructed, for example, using BBAMelfab 80 media, a fibrous polypropylene nonwoven media available fromBBA Fiberweb Terram Limited, Gwent, United Kingdom. The filter insert 8may be produced by pleating the Melfab 80 media and then heat settingthe pleats. Forming the pleats by heat setting may be accomplished usinga Rabofsky pleater with a 200° F. heat set platen temperature. Formingthe pleats in this media by heat setting produced a filter insert havingthe desired characteristics. That is, the filter insert 8 wasself-spacing and had the desired springiness such that when the filterinsert 8 was expanded to the length of the filter frame 2, the filterinsert 8 was under tension. Thus, when the filter insert 8 was expandedto a length greater than the length of the filter frame 2, the filterinsert 8 exhibited elastic recovery and therefore tended to recoil to alength less than the length of the filter frame 2.

Melfab 80 is nonwoven fibrous media formed of polypropylene fibers. Themedia has a thickness of approximately 0.63 mm, a basis weight of 80g/m², and a permeability of 690 cfm. The pleated filter insert had apressure drop of 0.13″ W.G. at a face velocity of 300 fpm, and apressure drop of 0.28 W.G. at a face velocity of 500 fpm.

To install the filter 8 into the frame 2, the frame 2 is placed on asurface so that the base 4 is beneath the cover 6. The frame 2 is thenopened as shown in FIG. 1 by releasing the latches 44 and pivoting thecover 6 upwardly away from the base 4. The filter 8 is then expanded bygrasping the attachment members 70 and separating them such that thepleats become spaced. The filter 8 is then placed in the base 4 so thatthe pleats 12 mesh between the ribs 32. The holes 76 in the attachmentmember 70 are then placed on the protrusions 48 to attach the filter 8to the base 4. The cover 6 is then closed to retain the filter 8 inplace, and the latches 44 are re-connected to lock the cover with thebase 4. Constructed in this manner, the media 10 is supported from theback which allows the dirty side of the media to be facing up whenchanging the filter 8, thereby resulting in less mess. The filter 8 isremoved from the frame 2 by reversing the above steps.

It will be recognized that the filter 8 may be attached to the cover 6rather than the base 4. In this manner, the ribs 32 move into the pleats12 as the frame 2 is closed. This, however, is less desirable becausethe pleats may require some adjustment to properly nest with the ribs32, and the dirty filter will be laying with the dirty side facing downduring replacement. This, in turn, will produce an unwanted mess.

It will be apparent to those of ordinary skill in the art that variouschanges and modifications may be made without deviating from theinventive concept set forth above. Thus, the scope of the presentinvention should not be limited to the structures described in thisapplication, but only by the structures described by the language of theclaims and the equivalents of those structures.

1. A self-spacing pleated filter insert for use with a frame having alength and a plurality of equally spaced transverse ribs that mesh withthe expanded pleats of the filter insert, said self-spacing pleatedfilter insert comprising a reversibly collapsible and expandableself-supporting fibrous nonwoven polypropylene filter media including aplurality of pleats formed by heat setting and are generally uniformlyspaced upon expansion and release of said pleated filter insert, whereinwhen said pleated filter insert is expanded to the length of the filterframe, said pleated filter insert is under tension, and when saidpleated filter insert is released, it will return to an equilibriumlength that is no greater than the length of the frame.
 2. A pleatedfilter insert as defined in claim 1, wherein said filter media has abasis weight of 50–80 g/m^(2.)
 3. A pleated filter insert as defined inclaim 2, wherein said filter media has a thickness of 0.5–0.63 mm.
 4. Apleated filter insert as defined in claim 3, wherein said filter mediahas a permeability of 690–1024 cfm.
 5. A pleated filter insert asdefined in claim 1, further comprising attachment members along opposedfirst and second ends of said filter media for securing said pleatedfilter insert into a frame.
 6. A pleated filter insert as defined inclaim 5, wherein said attachment members contain holes adapted to matewith respective projections on the frame.
 7. A pleated filter insert asdefined in claim 6, wherein said attachment members contain anasymmetric hole pattern that allows the pleated filter insert to beattached to the frame in only one orientation.